Injection systems with at least one injector and especially leakage-oil-free common-rail-injection systems demand a control element or an actuator, such as a piezoactuator for example, in the high-pressure chamber of the injector. The technical field of the invention relates in particular to piezo-controlled common-rail injectors or injection systems without leakage oil return with an actuator or an actuator for opening and closing a nozzle by means of an injector needle in the high-pressure chamber which features a hydraulic length compensation facility and a lever transmission for actuating the injector needle. The length compensation facility especially features a piston engaging in a hole of the base plate of the piezo stack of the piezoactuator, a hydraulic volume, for example a volume of fuel, between the base plate and the piston and a return spring for resetting the piezo stack. Such an injection system is for example known from DE 101 45 620 B4.
The function of the above-mentioned lever transmission is to translate the stroke provided by the piezo stack into a modified, especially increased, stroke. To this end the lever transmission generally features an actuator lever which is coupled to the piezoactuator and a needle lever which is coupled to the injector needle. The actuator needle and the needle lever form a two-stage lever facility which, as a result of its two-stage nature, needs a large mounting height. The applicant has established in a trial with such a lever transmission that on actuation of the lever the tipping moment initiated in the injector needle can result in a negative influence on the function. In particular a resulting lateral force acts on the needle during the lifting movement. This produces undesired friction forces in the needle guide which increase the energy required to lift the injector needle. It is also known internally to the applicant that this negative function influence can be corrected by means of an additional guide in the area of the needle shaft. However a force introduced off-center into the lever transmission leads to increased friction traces in the transition area of the modules, for example between needle lever and injector needle head of the injector needle. This produces high friction losses between these components, for example between the needle lever and the injector needle head. Disadvantageously these friction losses shorten the lifetime of the injection system. These friction losses also cause a loss of energy in the translation or transmission of the stroke provided by the actuator.